Modern telecommunication has experienced explosive growth in the past decade. Distinguishing from the conventional telecommunication systems, there are two important aspects in modern telecommunication technologies, one being digital, and another being wireless. Wireless communication revolutionarily changes the way of communication and provides possibility of communication to anyone, from anywhere, at anytime. While wireless communication technology significantly changes the way people live and work, it adds tremendous challenges to communication engineering design. It is obvious that when a radio signal is transmitted through the air, the signal quality will largely depend on many variables in communication environments that are beyond our control. For example, the radio signal could be absorbed by or reflected from the buildings, mountains, or other obstacles between two points of communication. In addition, the received signal quality depends on the speed of mobile transmitter and receiver terminals. All of these increase the difficulties of maintaining a quality communication link. Furthermore, unlike a wired communication system, a wireless communication system often has problems with flat or frequency selective fading, and time dispersion.
In order to maintain a quality wireless communication signal, the radio channel must be estimated and properly compensated, and one effective means of such channel estimation and compensation is called channel equalization. Due to the time-varying nature of a radio channel, channel equalization is often designed to be adaptive, or time-varying, in order to track dynamic channel variation.